The Xultun scribe’s chamber, with A, B, and C showing the locations of the calculations.

In a small closet-like chamber off a central plaza of the ancient Mayan city of Xultun, a scribe once sat with a paintbrush in hand.

On the north walls of the room, he painted an apparent self-portrait, facing a figure with an elaborate headdress, perhaps a ruler. But on adjacent walls, he and his successors, starting in about 800 C.E., painted and inscribed various astrological calculations. They are very similar to those found in the Dresden Codex, one of the most famous extant Mayan books, which contains numerous astrological and ritualistic cycles and is thought to have been copied from older books sometime between the 11th and 15th centuries. The markings on the scribe’s walls in Xultun, unveiled last week in a paper in Science, represent the earliest known depictions of some of these calculations.

The glyphs in location C, which consist of columns of dates

National Geographic, which helped fund the work, has a news feature on the discovery that gives perspective on the calculations’ purpose:

For ninth-century Maya, tabulating astronomical calendars to predict times of plenty was akin to gauging the stock market today, said [Mayan-writing expert David Freidel of Washington University in St. Louis], who wasn’t involved in the new study. When the mural was made, the Xultún region was facing “a period of intense drought. In fact, cities were collapsing in various parts of the Maya world in this era,” he said.

“The preoccupation of this king and his courtiers with astronomical calculation is not an arcane exercise. It has a very practical consequence for the people of the city of Xultún, which is, What the hell is going on with the economy?”